Red List habitat classification > RL - Marine habitats > RLNEA - Atlantic > NEAA5.32 Estuarine Atlantic sublittoral mud

Estuarine Atlantic sublittoral mud

Quick facts

Red List habitat type code NEAA5.32
Threat status
Europe Near Threatened
EU Near Threatened
Relation to
Source European Red List habitat factsheet
European Red List of habitats reports
European Red List of habitats (Excel table)


This habitat comprises shallow sublittoral muds, extending from the extreme lower shore into the subtidal in variable salinity (estuarine) conditions, typically in the range of 18-35ppt and extending to a depth of 10 m. The habitat is found within estuaries which are naturally highly dynamic and rapidly changing systems, forming a complex mixture of many different habitat types.  These habitats do not exist in isolation, but rather have physical, chemical and biological links between them, for example in their hydrology, in sediment transport, in the transfer of nutrients and in the way mobile species move between them both seasonally and during single tidal cycles.

Turbidity and the mobility of the sediment are important influences on the associated marine communities which may be impoverished where this is high. There are typically fewer macrobenthic speices than in fully marine areas but potentially with a high abundance and biomass. Such habitats typically support communities characterised by oligochaetes, and polychaetes and have a  dominance of deposit feeders In lowered salinity conditions the sediments may include a proportion of coarser material, where the silt content is sufficient to yield a similar community to that found in more heterogeneous muds. Migratory flatfish such as plaice, dab and sole move in to estuaries to feed in these habtiats. 

Indicators of Quality:

Long term studies of many estuaries typically focusing on the physical, biological and chemical characteristics.  Indicators of quality of this habitat are frequently linked to those for the whole estuarine environment and therefore include morphological and physical characteristics, carrying capacity and water quality parameters. For the specific habitat, benthic indices, contaminant levels and productivity are some of the frequently used measures of quality.

Indices developed to assess the ecological status of coastal waters, including estuaries, according to the Water Framework Directive, include physical indicators, water quality indicators and measures of benthic diversity, species richness and abundance. The latter group, which is particularly relevant to benthic habitats, includes a Benthic Quality Index, an Infaunal Trophic Index, a Marine Biotic index based on ecological groups, and the Benthic Opportunistic Polychaetes/Amphipods Index.

Characteristic species
For full habitat description, please download the habitat factsheet.

Threat status

Synthesis of Red List assessment

Survey information confirms that this habitat has a widespread distribution in the North East Atlantic. The precise extent is unknown however as EOO >50,000km2 and AOO >50, this exceeds the thresholds for a threatened category on the basis of restricted geographic distribution.
There is a lack of data on trends, however this habitat has been assessed as Near Threatened for the EU 28 and EU 28+ because of historical reductions in quality which are believed to have been fairly substantial. The main threats continue, although probably to a lesser extent, and there have been improvements in water quality which may have facilitated some recovery but there is insufficient information to predict future trends.
Red List Category Red List Criteria
Near Threatened C/D1, C/D3
Red List Category Red List Criteria
Near Threatened C/D1, C/D3

Confidence in the assessment

Red List of habitat categories and criteria descriptions

Pressures and threats

  • Urbanisation, residential and commercial development
    • Discharges
    • Disposal of household / Recreational facility waste
    • Disposal of industrial waste
    • Water discharges (with/without contaminants)
  • Pollution
    • Pollution to surface waters (limnic, terrestrial, marine & brackish)
    • Pollution to surface waters by industrial plants
    • Pollution to surface waters by storm overflows
    • Diffuse pollution to surface waters via storm overflows or urban run-off
    • Diffuse pollution to surface waters due to household sewage and waste waters
    • Input of contaminants (synthetic substances, non-synthetic substances, radionuclides) - diffuse sources, point sources, acute events
    • Marine water pollution
    • Toxic chemical discharge from material dumped at sea
    • Non-synthetic compound contamination
    • Synthetic compound contamination
  • Natural System modifications
    • Human induced changes in hydraulic conditions
    • Removal of sediments (mud...)
    • Estuarine and coastal dredging
    • Change of sea-floor substrate
    • Modification of hydrographic functioning, general
    • Wave exposure changes
    • Alteration of sea-floor/ Water body morphology
    • Siltation rate changes, dumping, depositing of dredged deposits
    • Dumping, depositing of dredged deposits
    • Other siltation rate changes
    • Dykes, embankments, artificial beaches, general
    • Sea defense or coast protection works, tidal barrages
    • Dykes and flooding defense in inland water systems
  • Climate change
    • Changes in abiotic conditions
    • Water flow changes (limnic, tidal and oceanic)
    • Wave exposure changes
    • Sea-level changes

Habitat restoration potential

The capacity for this habitat to recover once severely damaged is unknown.

Trends in extent

Average current trend in quantity

Decreasing Decreasing
EU28 EU28+

Trends in quality

Average current trend in quality

Decreasing Decreasing
EU28 EU28+

Conservation and management needs

Conservation and management schemes to benefit estuarine habitats have been applied at a number of scales ranging from whole estuary systems to small areas within an estuary. They include the removal of dykes, and water quality improvement programmes to reduce the risk of toxic contamination and to reduce nutrient inputs leading to eutrophication.
Spatial management including zoning of activities as part of Integrated Coastal Zone Management Schemes and Marine Protected Areas that cover the entire estuary complex, as well as management of water quality throughout the watershed, are beneficial.

List of conservation and management needs

  • Measures related to wetland, freshwater and coastal habitats
    • Restoring/Improving water quality
    • Restoring/Improving the hydrological regime
  • Measures related to spatial planning
    • Establish protected areas/sites
  • Measures related to urban areas, industry, energy and transport
    • Urban and industrial waste management


For each habitat a distribution map was produced from a wide variety of sources indicating known and potential occurrences of the habitat in 10x10 km grids within Europe. Occurrences in grid cells were given in two classes: actual distribution from relatively reliable sources (surveys, expert knowledge), and potential distribution based on models or less reliable indicators. Please download the fact sheet to see the map.

Geographic occurrence and trends

Seas Present or presence uncertain Current area of habitat (Km2) Recent trend in quantity (last 50 years) Recent trend in quality (last 50 years)
Bay of Biscay and the Iberian Coast Present Unknown Decreasing Decreasing
Celtic Seas
Greater North Sea

Extent of Occurrence, Area of Occupancy and habitat area

Extent of Occurrence (EOO) (Km2) Area of Occupancy (AOO) Current estimated Total Area Comment
EU28 1,999,917 187 Unknown EOO and AOO have been calculated on the available data. Although this data set is known to be incomplete the figures exceed the thresholds for threatened status.
EU28+ >187 Unknown EOO and AOO have been calculated on the available data. Although this data set is known to be incomplete the figures exceed the thresholds for threatened status.
AOO = the area occupied by a habitat measured in number of 10x10 km grid cells.
EOO = the area (km2) of the envelope around all occurrences of a habitat (calculated by a minimum convex polygon).

Characteristic species

Not available

Vegetation types

Relation to vegetation types (syntaxa)

Not available

Other classifications

Not available
European Environment Agency (EEA)
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1050 Copenhagen K
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